The present invention can be used in systems for monitoring and controlling the temperature of thermal processes in metallurgy, mechanical engineering industry, semiconductor technology, microelectronics, thermochemistry and glass production. An example of this is the use of the present invention for temperature monitoring of epitaxial growth of semiconductor layers in microelectronics, and for controlling thermal characteristics of local heating of rolled sheets in metallurgy and machine industry.
In all these arrangements, a problem arises both of evaluating the true temperature of an object at a particular selected point on its surface and of obtaining a true temperature profile over the entire surface of the object, taking into account non-uniformity of this surface as regards its emissivity (considering film structure of varying thickness, oxide films, scale, heterogeneous materials, etc. present on the surface of the object) and variation in sensitivity over the target area of camera tubes and television cameras. Another difficulty with such known arrangements resides in the fact that their readings, i.e. the temperature measurement results, are dependent on the distance between the object under investigation and the television camera, upon the absorbing properties of the intervening medium therebetween (different windows, water jackets, metal grids, dustiness of the gaseous medium, etc.), and upon the parameters of the video amplifier employed (i.e. its amplitude-frequency response).
Known in the prior art is an arrangement for measuring the object temperature (cf. U.S.S.R. Inventor's Certificate No. 409088) comprising an optical system through which radiation from an object is projected onto the photocathode of a television camera. The video signal generated by the TV-camera is applied to the input of a television receiver which delivers frame and line synchronizing pulses to a means for sampling a selected line video signal. As the selected line number is counted off, its video signal is amplified and applied to the additional vertical deflection coils or plates of the picture tube in the television receiver, the brightness level of the beam being increased for the period of line duration. A local temperature distribution pattern (or temperature profile) of an object is continuously displayed on the screen together with the image of the object following the points lying on the dark path of the selected line.
This arrangement provides visual information on the temperature profile only along a particular line on an object.
This arrangement, however, tends to introduce a considerable error on account of the subjective character of reading the temperature of the object by its temperature profile slot and owing to low accuracy of the devices shaping this temperature profile.
In another known arrangement for measuring temperature of a heated object (cf. FRG Patent No 1473258) comprising a TV-camera connected, via amplifying stages, to a colour television receiver, a signal is generated in the amplifying stages and a particular colour assigned to individual points of the object image on the screen depending on the temperature of the respective points on the surface of the object, thus allowing observation of isothermal lines and areas distributed over the object surface. A quantitative measure of the isotherm temperatures is given by the images of reference radiation sources of known temperature exhibited on the screen of the TV-receiver. By comparing the colours of the images of the reference source and the object under investigation, the temperature of the latter is obtained.
The principle of generating colour signals of the thermal image in this arrangement is based on amplitude discrimination of the video signal generated by the television camera which suffers from a disadvantage residing in variation of sensitivity over the field of the image being generated, which entails appreciable errors when this arrangement is used for measuring the temperature of the object under investigation (even if the object does not exhibit a non-uniform emissivity feature).
There is known a system for reducing the effect of background shading introduced by variation in sensitivity over the target area of a camera tube (cf. U.S. Pat. No. 3,902,011) comprising a TV-camera and a video monitor connected through a video amplifier, the signal thereof being corrected under control of an electronic computer comprising a multiple location store for storing the shading correction signal, an interpolator means for interpolation of storage correction values, a device for automatically storing the correction signal in locations of the store for a period of several scanning frames.
This prior art system allows a true and reliable reproduction of uniformly illuminated (i.e. uniformly heated) images of the object on the video monitor screen.
In order that the system be programmed, i.e. information concerning the desired correction signal be inserted into the store, a reference source of a perfectly uniform temperature field is required. But the provision of a reference source with a sufficiently large area of radiating surface and a constantly uniform distribution of emmisivity thereover presents certain difficulties. And consequently, the overall accuracy of temperature profile analysis is affected. Mover, even the systems ensuring most satisfactory visual images of thermal or temperature profiles fail to provide a sufficiently accurate quantitative estimation of the temperature drop in at least two points of the profile due to the subjective character of this estimation.
Known in the art is an arrangement for measuring the temperature difference between the points of an object displayed on the screen of the cathode-ray tube (cf. U.S.S.R. Patent No. 303812) comprising a camera generating a video signal, a change in intensity thereof corresponding to a change in point temperatures of the object under investigation, a video amplifier which amplifies the video signal, a means for controlling brightness of the cathode-ray beam, a manual adjustment device coupled to the brightness control means. The manual adjustment device serves to sequentially fix the brightness level of any two visually compared image points of the object under investigation. As a result, a dial mechanically coupled to the brightness control knob allows a direct evaluation of the temperature difference between two selected points on an object.
This known arrangement, however, lacks accuracy of evaluating the object temperature due to the subjective character of this evaluation. It exhibits a poor reliability of mechanical devices and fails to provide a sufficient accuracy in locating the object points to be monitored.
Known in the art is a radiation monitoring system (U.K. Patent No. 1,357,940) comprising an optical system for focusing thermal radiation emitted by an object under investigation, a reference lamp with an associated prism arrangement employed for calibration of the system, a TV-camera responsive to thermal radiation from the object and the reference lamp to produce a video signal proportional to their thermal radiation density, a television monitor with its input connected to the output of the TV-camera, a means for generating the gating marker, the input thereof being connected to the synchronizing output of the TV-camera and the output connected to the first information input of the television monitor, a means for sampling and measuring the video signal amplitude with its signal input connected to the output of the TV-camera and its control input connected to the output of the gating marker generating means, a character generator with its synchronizing input connected to the synchronizing output of the TV-camera and its output connected to the second information input of the TV-monitor, and a computer with its output connected to the input of the character generator and the input electrically connected to the output of the means for sampling and measuring the video signal amplitude.
This system provides an objective temperature measurement of the object under investigation at any point on its surface specially indicated by a movable dot, or marker, on the screen of the TV-monitor.
This system, however, lacks accuracy in measuring the temperatures at different points on the surface of the object under investigation, the images of which are positioned at different points of the television raster, this inaccuracy being due to the following factors: variations in sensitivity at different points on the target of the TV-camera tube (as much as 15%) and inadequate adjustment for these variations by means of the reference lamp with the associated prism arrangement; variations in emissivity of the surface of the object under investigation which cannot be adjusted by the reference lamp, its filament ultimately exhibiting a varying emissivity; the resulting measurements are influenced by the distance from the object under investigation and the TV-camera, which necessitates recalibration of the system or correction of its measurements in case the distance is changed; the resulting measurements are influenced by the absorbing properties of the intervening medium between the object and the TV-camera; the resulting measurements are influenced by the parameters of the optical system (i.e. aperture ratio of the lens employed and its focal distance), which necessitates recalibration of the system or appropriate correction provided therein in case the optical system is changed; the resulting measurements obtained by means of the system are influenced by the parameters of the TV-camera video amplifier (i.e. its amplitude-frequency response) thus preventing a true and reliable measurement of the temperature of objects which are small in size when displayed on the screen of the TV-monitor.